Known housings for electronic components, for example, QFN (quad flat no leads) housings comprise leadframe sections, for example, as basic material. The QFN housings are also designated as QFN packages and/or as micro leadframe (MLF) and are known in electronics as a chip housing design for integrated circuits (IC). The designation “QFN” encompasses different sizes of IC housings which can all be soldered as surface-mounted devices on printed circuit boards. The designation “QFN” is also used as representative of the following designations: MLPQ (Micro Leadframe Package Quad), MLPM (Micro Leadframe Package Micro), MLPD (Micro Leadframe Package Dual), DRMLF (Dual Row Micro Leadframe Package), DFN (Dual Flat No-lead Package), TDFN (Thin Dual Flat No-lead Package), UTDFN (Ultra Thin Dual Flat No-lead Package), XDFN (eXtreme thin Dual Flat No-lead Package), QFN-TEP (Quad Flat No-lead package with Top Exposed Pad), TQFN (Thin Quad Flat No-lead Package), VQFN (Very Thin Quad Flat No Leads Package). As an essential feature and in contrast to the similar Quad Flat Package (QFP) the electrical connections (Pins) do not project laterally beyond the dimensions of the plastic enclosure of the housings, but rather are integrated in the form of non-tin-plated copper connections into the underside of the housing in a planar fashion, which copper connections can be formed, for example, by the undersides of the leadframe sections. As a result, the required space on the printed circuit board can be reduced and a higher packing density can be achieved. Furthermore, a particularly good heat dissipation toward the printed circuit board can be ensured.
The leadframe sections are singulated from leadframes. The leadframes comprise, for example, an electrically conductive material, for example, copper or are formed therefrom. The leadframe sections serve, for example, to mechanically fix and/or electrically contact electronic components such as, for example, chips, for example, semiconductor chips and/or components that emit electromagnetic radiation. For this purpose, the leadframe sections have, for example, receiving regions that receive the electronic components and/or contact regions to electrically contact the electronic components.
During production of the housings, the leadframes are embedded into a molding material, for example, in a molding method, for example, an injection molding or transfer molding method. The molding material can be a plastic enclosure. The structure comprising molding material and the leadframe embedded therein can also be designated as a housing arrangement. The fact that the leadframes or leadframe sections are embedded into the molding material means, for example, that the leadframes or the leadframe sections are at least partly surrounded by the molding material. Parts of the leadframes can remain free of molding material, for example, at an underside of the leadframes the electrical connections that contact the housings, in particular the leadframe sections of the housings and/or, for example, at a top side of the leadframes the receiving openings in which the receiving regions and/or contact regions are exposed. The electrical contacts of the housings are formed at an opposite side of the leadframe sections relative to the receiving regions. By way of example, the electrical contacts are formed by the undersides of the leadframe sections. As a result, the finished housings can be placed onto a printed circuit board, wherein directly by the resultant physical contact between the housing and the printed circuit board it is also possible to produce the electrical contact with the leadframe section and the electronic component contacted therewith and/or a thermal coupling of the housing or of the electronic component to the printed circuit board.
During the embedding of the leadframe into the molding material, the housing assemblages formed by molding material and leadframe and/or the corresponding housings can warp, for example, on account of material shrinkage and/or on account of thermal expansion. In such warped housing assemblages and/or housings, problems can arise during subsequent processing processes. By way of example, the warped housing assemblages may be handled relatively poorly on roller conveyors, magazine inlets or outlets and/or when sucked up on a vacuum table.
One cause of bending resides, for example, in the different coefficients of thermal expansion (CTE) between the material of the leadframe and the material of the molding material which can comprise, for example, a thermosetting plastic, for example, epoxy resin, silicone resin or a thermoplastic, for example, PPA or polyester. The CTE of the molding material, above the glass transition temperature, is generally higher than that of the material of the leadframe and, below the glass transition temperature, is generally below the CTE of the material of the leadframe. On account of these differences in the coefficients of thermal expansion, the bending described above arises, for example, in a manner corresponding to the known bimetal effect.
To avoid bending of the housing arrangement and/or of the housing, it is known to use epoxy-based resins, for example, as molding material, for example, an EMC (electro mold compound), the CTEs of which below their glass transition temperature are 7 ppm/K to 12 ppm/K, for example, and to use for the material of the leadframes, for example, an FeNi alloy, for example, alloy 42 having a CTE of approximately 8 ppm/K. With the use of these materials, the warping can be kept small, but not prevented, in the case of the housing arrangement. In many applications, for example, in housings for components that emit electromagnetic radiation, however, leadframes having high thermal conductivity, for example, composed of copper may be desired.
Furthermore, in order to reduce warping it is known to reduce the thickness of the molding material on the leadframes as far as possible. Furthermore, to reduce warping it is known to form two molding material regions on a leadframe which are spaced apart from one another in the center such that the leadframe is free of molding material between the two molding material regions. Furthermore, during the subsequent processing processes, pressure rollers can be used, for example, to press the bent housing assemblages onto the corresponding transport means.